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Running bad all the time, losing coolant, strange deposit on #1 plug. Hmmmmm No it's not a common "Jeep thing" but strange things happen to all makes. I'm thinking a cracked head could leak coolant into the intake valve area, above the valve, so the engine could indeed "suck coolant". cracks open and close some with temp changes and properties would change as the crack grew with time.

The O2 sensor should not affect the way the engine runs cold, it's out of the loop so to speak. I would talk about the fuel system but that would have nothing to do with coolant loss.

If what is said is true, coolant loss with no external leaks, I'll guess cracked head. <img src="/forums/images/graemlins/notooth.gif" alt="" />


These all have cast iron heads right? I mean I know its not impossible, but it just seems unlikely that one cracked.

Question though, why would an O2 sensor be out of the loop when the engine is cold? And have things changed because on my 99 I can watch the output of the O2 sensor with a scan tool and my laptop, and I can also watch the status of the fuel system, and the only time it says it runs in open loop is at wide open throttle, and under decel with the throttle closed.